Due to a mechanism not entirely understood by physicians the cardiovascular blood delivery system often becomes less efficient as one ages. Although the causes of arteriosclerosis are not completely understood, one symptom is the partial or, in extreme cases, the total blockage of a blood vessel due to a build up of deposits along an inner surface of the blood vessel.
Prior art proposals recognize that one possible procedure for treating a condition of partially or totally blocked blood vessels is to open the blocked blood vessel. One such prior art technique for reopening a blocked blood vessel is to insert a balloon catheter within the vessel to expand the vessel and either break loose deposits within the vessel or alternatively, increase the size of the lumen passing through those deposits.
An alternate proposal for opening a blocked vessel is to bring a high-speed rotating device into contact with occluded portions of the blood vessel. The rotating device produces cutting, abrading, or fluid turbulence to open the vessel and increase blood flow. One device for physically opening the blood vessel in this manner is disclosed in U.S. Pat. No. 3,762,416 to Moss entitled "Improvements In or Relating To Drills for Clearing Obstructions". In this patent, a high-speed motor rotates a flexible drive shaft connected to a cutting bit. The bit and flexible drive shaft are inserted into an occluded blood vessel so that when the bit is rotated at high speed and moved into contact with occluded regions it breaks loose deposits within the blood vessel.
A more recent prior art patent disclosing a similar system for blood vessel cannulization is disclosed in U.S. Pat. No. 4,445,509 to Auth entitled "Method and Apparatus for Removal of Enclosed Abnormal Deposits". This patent describes a differential cutting tool inserted into an occluded blood vessel. Again, high speed rotation of the cutting tool causes the tool to remove abnormal deposits from inside the blood vessel.
U.S. Pat. No. 4,589,412 to Kensey entitled "Method and Apparatus for Surgically Removing Remote Deposits" discloses a procedure for removing atherosclerotic plaque. A cutting tip is rotated by the application of fluid pressure through a multi-lumen catheter. U.S. Pat. No. 4,747,821 to Kensey et al, which issued May 31, 1988 also discloses a catheter that includes a rotating cutting head at its distal end.
At the distal end of the catheter disclosed in the '821 patent a specially configured rotatable cutting tip is supported within a bearing fixed to the flexible catheter and having axially extending grooves which provide a fluid communication path from the center passageway of the catheter to the subject blood vessel. As the rotatable cutting tip of the '821 catheter rotates, these grooves are periodically exposed. Fluid passing down the interior region of the catheter under pressure exits the catheter via these grooves and in this way, an opaque dye can be injected into the blood vessel, thereby allowing an attending physician to monitor progress of the cutting tip as it is rotated.
Experience with a catheter similar to that depicted in the '821 patent to Kensey et al indicates that when boring through fatty or fibrous tissue, tissue that is partially or totally separated from the vessel can enter the longitudinal or axially extending grooves in the bearing that rotatably supports the cutting tip. This not only clogs the passage of fluid from the center region of the catheter, but can also cause the material to wind around the cutting head. This causes the catheter to bind and in some instances can even cause the flexible drive shaft to break. The physician conducting the procedure must then withdraw the catheter from the subject even though the vessel may not be adequately treated. Additionally, if tissue becomes wound around the cutting tool, but remains attached to the vessel wall it may pull on the interior wall linings of the vessel and seriously damage the vessel.